The field of the invention pertains to hand operated mechanical torque wrenches and in particular to torque wrenches that may be preset to give a sudden audible and sensual signal when the present torque is reached. Such torque wrenches are commonly used on assembly lines by relatively unskilled workers to assure that threaded fasteners are repeatedly set to the proper torque.
The wrenches utilize a camming mechanism that suddenly releases when the preset torque is reached. The mechanisms generally fall into two categories, i.e., pivotally attached camming members and free floating camming members. Examples of pivotally attached camming members are illustrated by the pinned rollers of U.S. Pat. Nos. 2,918,834, 3,140,623, 3,165,014, 3,270,594, 3,577,815 and Re. 25,547. A ball retained within a socket as the camming member is also disclosed in U.S. Pat. Nos. 2,786,378 and 3,165,014 and British Pat. No. 966,947. Examples of the free floating camming members are illustrated by the rectangular and trapezoidal pawls of U.S. Pat. Nos. 2,743,638, 2,897,704 and 3,016,773.
The pinned roller wrenches are generally more complicated and therefore relatively expensive to manufacture and service. The ball in socket wrenches eliminate some of the complication, however, point contact and sliding movement over some portion of the camming action results in high surface stresses on the ball and engaging member. A short tool life occurs between of wear caused inaccuracy. Rebuild or replacement is then required. Similarly, the sharp corners on the free floating pawls are subject to wear with a resulting relatively short tool life because the accuracy of the wrench is greatly reduced. To counteract the wear problems, in many instances, wrenches of a larger size with a greater range than necessary for a particular application are purchased so that they may be set to a torque level below the maximum level for the wrench and thereby obviate the wear problem. Such an approach is obviously unnecessarily expensive.